This invention relates to seals, especially for flange connections and even more especially for connections between glass lined flanges.
Gaskets for sealing flanges together are well known in the art. Unfortunately, readily removable and cost effective gaskets for sealing flange faces have not been as good as desired, especially when the flange faces have been glass coated and surround openings in vessels or conduits having corrosive contents that are under pressure, e.g. 300 psi (about 20 atmospheres) or higher. Under such conditions, seals between flange faces have often been known to leak or even blow out. Further, such known gaskets require high seating loads that can cause glass lining failures. Such seals also require a large number of clamps or bolts in a uniform distribution around the seal area in order to maintain the high loads required.
Known seals, for glass and other smooth surfaces, generally use gaskets having flat surfaces that can seal at almost any location on the surface. Such seals are not as sanitary as desirable for pharmaceutical and food applications because of cracks at the edge of the contact areas between the sealing flange and gasket that can harbor contamination because the actual seal may be formed at another location on the flat gasket surface.
It has been known to use O-rings to form seals between flange faces; however, to prevent "blowout", grooves have been needed in the flange faces in order to position and retain the O-rings, especially when any significant pressure is involved. In the case of glass lined flange faces, such grooves cannot practically be used because the glass tends to crack at the sharp bends needed to form the grooves.
The use of a polytetrafluoroethylene (PTFE) ring gasket to provide supplemental support for an O-ring has been considered; however, PTFE does not have sufficient dimensional stability either to retain the O-ring against radial blow out or to retain a dimensionally stable groove to hold the O-ring.
In response to the above problems, an O-ring envelope gasket was invented and awarded U.S. Pat. No. 5,556,113. This gasket is provided with a fluoropolymer protective sheet that covers, protects and retains an O-ring supported by a reinforcing ring comprising a metal strip between compressible layers. The metal ring in this gasket provides significant resistance to radial deformation or rupture ("blow out"). While gaskets, as described in U.S. Pat. No. 5,556,113, are an improvement over prior gaskets for sealing glass coated flanges, they are complex to manufacture. Furthermore, the metal supporting ring and compressible layers may not have sufficient corrosion resistance to withstand attack by the contents of the container in the event that the relatively thin protective sheet is breached. It is therefore an object of the present invention to eliminate or reduce the above described problems and disadvantages associated with prior sealing gaskets for flanges, especially glass lined flanges.